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N A T A L I A D I M A R C O
L A B O R A T O R I N A Z I O N A L I D E L G R A N S A S S O - I N F N
O N B E H A L F O F T H E N E W S C O L L A B O R A T I O N
NEWS: Nuclear Emulsions for Wimp Search
Italy • Napoli University “Federico II” • LNGS – INFN • Bari University • Roma University “La Sapienza”
Japan • Nagoya University • Chiba University
Russia • JINR Dubna • Moscow State University • Lebedev Physical Institute
Turkey • METU, Ankara
Directional DM searches
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• Solar system movement in the galaxy WIMP Flux not isotropic @ Earth.
• Directional measurement as a strong signature and unambiguous proof of the galactic DM origin
D.
N.
Sp
erg
el,
Ph
ys.
Rev
. D
37
(19
88
)
Nuclear emulsion
Target nuclei
DM
DM
Direction of solar system (230km/sec)
earth@summer
earth@winter
DM wind
Current approach: low pressure gaseous detector
Targets: CF4, CF4+CS2, CF4 + CHF3
Recoil track length O(mm)
Small achievable detector mass due to the low gas density
⇒Sensitivity limited to spin-dependent interaction
DRIFT @ UK
DM-TPC@ USA MIMAC@ France
NEWAGE@ Japan
The NEWS idea
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Use solid target:
Large detector mass
Smaller recoil track lenght O(100 nm)
Nuclear Emulsion based detector acting both as target and tracking device
NIT: Nano Imaging Tracker , AgBr crystal size ~ 40 nm Natsume et al, NIM A575 (2007) 439
Read-out of submicrometric tracks
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1) Signal preselection
2) Signal confirmation
Resolution: 200 nm Speed: ~20 mm2/h
Resolution: 30 nm Speed: ~ (200μm)2/100 s
Direction detected!
θ
σ2 = σ2intrinsic+σ2
scattering
σ2 = 350 mrad
190 nm
signal
Width, nm
Ell
ipti
cit
y
80 keV C ions
σ = 235 mrad = 13°
Neutron test Beam
Read-out of submicrometric tracks
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Efficiency versus track length
Efficiency versus C energy
ε ~ 100% above ~200 nm
e > 1.25
MC data
171
nm
281
nm
1.1 μm 1.1 μm
Elli 1.48 Elli 1.68
Read-out of submicrometric tracks
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Read-out of submicrometric tracks
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0 30 60 90 120 150 180-1
-0.5
0
0.5
1
偏光板角度
pixe
l 58
nm
-1 -0.5 0 0.5 1-1
-0.5
0
0.5
1
dx (pixel 58nm)
dy
(p
ixel
58
nm
)
Resolution O(10nm)!
1) Signal
preselection:
optical
microscope
+
shape analysis 1μm 1μm
Polarization angle
2) Signal
confirmation:
optical
microscope
+
polarized light
e= 1.27
Expected Background
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Environmental radioactivity
Radon and its progeny
Cosmic rays
Neutrons from natural fission, (a,n) reactions and from cosmic ray muon spallation and capture
Radioimpurities in detector or shielding components
Intrinsic Neutron Yield
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Intrinsic radioactive contaminant contribution have been estimated @LNGS using: 1. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Chemistry Service) 2. g-spectrometry with Ge detector @ STELLA Facility (SubTErranean Low Level Assay)
Activity measured with ICP-MS: 238U: 23±7 mBq/kg 232Th: 5.1±1.5 mBq/kg
F. Pupilli et al. ,
arXiv:1507.03532
SOURCES-based simulation: 1.2 n/kg/year G4-based MC: 20.4% of neutrons interact producing nuclear (56%), proton (44%) and a (0.2%) recoils
Cut on the track lenght:
5%÷10% of the intrinsic neutron flux contributes to the background
A further reduction of 70% can be achieved exploiting the directionality information (-1 <F < 1) 0.02 ÷ 0.03 n/year/Kg
Experimental Set-UP
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1. Internal phere: 30 cm diameter, holding the target.
1 kg: 100, 50 mm thick,
NIT films
25 x 25 x 0.5 cm3
+ OPERA-like films
1. Plexiglass/nylon sphere: sealed from air and flushed with HP N2
2. External sphere: 50 cm thick PE shielding
Declination Axis
Polar Axis
3 2
Target: 1 Kg of NIT Shielding: 4 ton
Wimp’s wind
Experimental Set-UP
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Water Option
Schedule for 1 Kg Pilot Experiment
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Physics Reach
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NIT detector: 1 kg x 1 year
Zero background hypothesis
Directionality not included
Conclusions
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A novel approach for directional Dark Matter searches is proposed in NEWS
Novel nuclear emulsion technique with nanometric spatial resolution
The use of a solid target would allow to explore the low cross section sector in the phase space indicated by recent direct search experiments but using a complementary an powerful approach
Breakthrough in optical microscope readout technologies
Current level of neutron background from intrinsic radioactivity allows the design of ~ 10 kg detector
Prepare a kg scale (pilot) experiment soon (2018) as a demonstrator of the technology and the first spin-independent search of this kind
Letter of Intent submitted to INFN
Thanks for your attention!
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55 physicists
16
backup
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Directional DM searches
F. Mayet, J.Phys.Conf.Ser. 469 (2013) 012013
Depending on the unknown WIMP-nucleon cross section, directional detection may be used to : exclude Dark Matter, discover galactic Dark Matter with a high significance or constrain WIMP and halo properties.
PRODUCTION PROCESS
Crystal formation
thermobath
AgNO3 KBr
Control the AgBr crystal size
Temperature, insertion speed
Concentration of chemical, pAg control,
rotation speed
etc.
wash/salt reduction
Chemical for precipitation
Reduction of other salt
emulsion AgBr precipitate with gelatin
Gelatin solution
NO3- K+
Apply
Base film
Control of dry condition Temperature, humidity, Thickness etc.
Nuclear Emulsion
emulsion
AgNO3+KBr → AgBr↓+KNO3
K+ NO3-
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PRODUCTION IN NAGOYA
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Addition of AgNO3 and NaBr
AgNO3+NaBr → AgBr + NaNO3
control of AgBr crystal size, density
Emulsion Production
Desalination
Reduction of Na+, NO3 -
Sensitization
Au+ S sensitization
→tuning of the sensitivity
(grains/microns at given dE/dx)
NUCLEAR EMULSION PRODUCTION
500nm
35nm crystal 70nm crystal 100nm crystal 200nm crystal
For dark matter
Production time: 4h ~100g/batch
⇒ ~1 kg/week detector production
Size
R&D
Mr. Kuwabara
FujiFilm Engineer
Natsume et al, NIM A575 (2007) 439
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ULTRA-NANO IMAGING TRACKER
NIT U-NIT
AgBr
density
12
AgBr/µm
29
AgBr/µm
Range
threshold
Carbon Energy
200 nm 75 keV
100 nm 35 keV
50 nm 15 keV
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Physics Reach
23
Expected angular distribution
example with M = 25 GeV • Range > 150 nm
30°
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10000
1000
100
10
1
0.1
0.01
TS(TTL)
1983
NTS(CPLD)
1994
UTS(FPGA)
1998
S-UTS
(FPGA)
2010
Running
HTS (GPGPU)
2011- Development
0.003
0.082
1
72
9000
0.001
Speed in cm2/ hour ~2000m2/year
~20m2/year
24
Evolution of the scanning speed
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TECHNOLOGY DEVELOPMENT @ INFN
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OPTICAL MICROSCOPE READ-OUT: STEP 1
Scanning with optical microscope and
shape recognition analysis
Bonito CL/CMC-4000
CMOS Camera
4 Mpix, @100 fps
100W
Halogen
Lamp Nikon Oil Objective
100x, 1.45 N.A., Plan Apo
Magnifying lens,
Nikon VM C-2.5x
Resolution: 28 nm/pixel
View Size: 65.2 x 48.3 µm2
100x objective lens with
high N.A.
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SELECTION OF C ION TRACKS WITH SHAPE ANALYSIS
Direction detected!
θ
Signal selection:
• Major/minor>1.25
• width > 190 nm
σ2 = σ2intrinsic+σ2
scattering
σ2 = 350 mrad
190 nm
signal
Width, nm
Ellip
tici
ty
80 keV C ions
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SELECTION OF C ION TRACKS WITH SHAPE ANALYSIS
Direction detected!
θ
Signal selection:
• Major/minor>1.25
• minor > 170 nm
σ2 = σ2intrinsic+σ2
scattering
σ2 = 360 mrad
60 keV C ions
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INTRINSIC ANGULAR RESOLUTION AS A BY-
PRODUCT OF THE NEUTRON STUDIES
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NEUTRON TEST BEAM @ FNS (JAPAN)
Emitted neutron energy
En =Ei
82 +
19.6
Ei (MeV)+ cos2qn +cosqn
æ
èçç
ö
ø÷÷
2
Japan Atomic Energy Research Institute
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NEUTRON TEST BEAM ANALYSIS
Ep = 1.55 MeV
10mm
dE/dx
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NEUTRON TEST BEAM ANALYSIS
0.65 µm
Ep = 65 keV
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INTRINSIC ANGULAR RESOLUTION
σ = 235 mrad = 13°
• Neutron test Beam sample (FNS exposure)
• Compare clusters with elliptical (e > 1.1) shape
with the proton recoil direction
• Scattering contribution negligible
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2.8 MEV NEUTRON ENERGY MEASUREMENT
0
10
20
30
40
50
60
70
80
0,4 0,6 0,8 1
reco
il pro
ton
en
ergy[M
eV
] (SR
IM)
len
gth[μm
]
scattered angle cos(3D angle)
2.8
1.5
2.0
0.8
2.5
neutron energy 2.8±0.2MeV
resolution(σ/E) = 7%
• Measurement of track length and angle
• Proton energy using the energy-range relation (SRIM)
• Neutron energy
En= Ep / cos2ϑ
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Fluorescent molecule
Using fluorescence
Eric Betzig et al., Science 313, 1642 (2006)
Optical resolution ~10 nm
COS-7 cell optical images
100nm
IMAGING BEYOND OPTICAL RESOLUTION:
2014 NOBEL PRIZE IN CHEMISTRY
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RESONANT LIGHT SCATTERING FROM AG NANOPARTICLES
Oscillation of e-cloud Nano-metal in medium εd
Scattering spectrum depends on the light polarization and on the grain shape
0)(2)(
)(3EE
dm
dl
El intensity of inside metal
0)(2)( ldlm
H.Tamaru et al ., Applied Phys Letters 80, 1826 (2002)
El is resonance enhanced
The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy
SEM image SEM image
Ag 100 nm spherical
no polarizing property
Ag 100 nm spheroidal
polarizing property
λl
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SILVER GRAINS BUILDING UP TRACKS
30keV Carbon ion vertical implanted
Surface of emulsion 500nm
Shape different from each other
Scat
teri
ng
inte
nsi
ty
polarization direction of incident light
Optical response strongly depends
on the polarization of incident light
TEM image of Carbon track after development
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SILVER GRAINS BUILDING UP TRACKS
30keV Carbon ion vertical implanted
Surface of emulsion 500nm
Shape different from each other
Scat
teri
ng
inte
nsi
ty
polarization direction of incident light
Optical response strongly depends
on the polarization of incident light
TEM image of Carbon track after development
polarization direction
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SILVER GRAINS BUILDING UP TRACKS
30keV Carbon ion vertical implanted
Surface of emulsion 500nm
Shape different from each other
Scat
teri
ng
inte
nsi
ty
polarization direction of incident light
Optical response strongly depends
on the polarization of incident light
TEM image of Carbon track after development
polarization direction
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MICROSCOPE UPGRADE
Rotate by 180° with 10° steps
change the direction of polarization and measure the track
polarizer below the camera, rotated to charge polarization
Band-path filter
Sample
Camera
mirror
Polarizer
Obj. lens NA1.4
Xenon-Mercury Lamp
λ~550nm
Optical system
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MEASUREMENTS WITH RESONANCE EFFECT
255
0
Implant
3μm
1μm
Images with different polarization
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X
X
X
i=0
i=90
i=180
X0
X90
X180
X
Y
Evaluation of the position accuracy with a single grain
MEASUREMENTS WITH RESONANCE EFFECT
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A TRACK MADE OF TWO GRAINS
-3 -2 -1 0 1 2 3-3
-2
-1
0
1
2
3
dx (pixel 58nm)
dy
(p
ixel
58
nm
)
1μm
e = 1.49
without polarizer
Linear fit slope = track direction
0 30 60 90 120 150 180-3
-2
-1
0
1
2
3
偏光板角度
pix
el
58
nm
dx ● dy ○
1μm
Angle of polarization (degree)
Track validated by
elliptical shape analysis
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A TWO-GRAINS TRACK
1μm 1μm
0 30 60 90 120 150 180-1
-0.5
0
0.5
1
偏光板角度
pix
el
58
nm
-1 -0.5 0 0.5 1-1
-0.5
0
0.5
1
dx (pixel 58nm)
dy
(p
ixel
58
nm
)
Angle of polarization (degree)
dx ● dy ○
Position accuracy of a grain Track direction
e = 1.27
without polarizer
Discarded by
ellipticity cut (1.4)
Track length = 90 nm
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SINGLE GRAIN FOR ACCURACY EVALUATION
-1 -0.5 0 0.5 1-1
-0.5
0
0.5
1
dx (pixel 58nm)
dy (
pix
el
58nm
)
1μm
Ag 60nm
0 30 60 90 120 150 180-1
-0.5
0
0.5
1
偏光板角度
pix
el
58
nm
dx ● dy ○
1μm
Position accuracy of one grain
Polarization angle (degree)
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POSITION ACCURACY
σX = 10 nm σY = 10 nm
Unprecedented accuracy of 10 nm achieved on both coordinates
Breakthrough
(pixel size 28 nm)
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Target options
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NIT em MIP em Base MIP em NIT em
1sc 2dc 3dc 4dc 5sc
3)
1)
Muon
2) Wimp’s
wind MIP em. NIT em.
NIT
1 kg: 100, 50 mm
thick, NIT films
25 x 25 x 0.5 cm3
Equatorial Telescope
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• Mechanics:
2 motorized axes (Polar and Declination ) equipped with precise encoders for position monitoring. (Final precision 1°)
• Surface Calibration 1. Follow the position of a star in the Cygnus constallation; measure position
parameters in order to apply corrections to mechanics and electronic system.
2. Use throughout the whole day to study systematic effects.
• Underground installation Align the mount using existing high precision reference points.
• Materials screening of all the materials used in the telescope is foreseen in order to evaluate their intrinsic radioactivity. West
East
Polaris
South North
49
g background
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Electron rejection power
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hole+ electron-
Signal event (recoiled nuclei)
de/dx : 100~1000 keV/mm
Background event (electron) de/dx : 1~10 keV/mm
A rejection power O(106) is needed: • Chemical treatment (Tetrazolium-compounds) • Cryogeny • Discrimination in the read-out phase
51
a particles
Sources: 238U, 232Th chains and 222Rn
3D track range discrimination
Neutron production throught (a,n) reactions
SRIM simulation
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Environmental neutron flux
Light materials are effective moderators for fast neutrons: 50 cm of polietilene (PE, C2H4) reduction in the neutron flux of a factor O(104) The opportunity to add a thin (1÷2 cm) layer of Cadmium to capture thermalised neutrons is under study.
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Intrinsic neutron yield The intrinsic emulsion radioactivity is responsible of an irreducible neutron yield through (a, n) and 238 U spontaneous fission reaction Intrinsic radioactive contaminant contribution have been estimated @LNGS using: 1. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) (Chemistry Service) 2. g-spectrometry with Ge detector @ STELLA Facility (SubTErranean Low Level Assay)
1) ICP-MS: 238U: 23±7 mBq/kg 232Th: 5.1±1.5 mBq/kg
N. Marco TAUP 2015
Intrinsic neutron yield
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F. Pupilli et al. , Intrinsic neutron background of nuclear emulsions for directional Dark Matter searches, to be submitted to Astrophysical Journal
Intrinsic neutron yield
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GEANT4 simulation:
20.4% of neutrons interact producing nuclear (56%), proton (44%) and a (0.2%) recoils
Intrinsic neutron yield
N. Marco TAUP 2015 57
• 5%÷10% of the intrinsic neutron flux contributes to the background
• A further reduction of 70% can be achieved exploiting the directionality information (-1 <F < 1)
0.02 ÷ 0.03 n/year/Kg